INHIBITION OF THE RELEASE FACTOR-DEPENDENT TERMINATION REACTION ON RIBOSOMES BY DNAJ AND THE N-TERMINAL PEPTIDE OF RHODANESE

A peptide consisting of the 17 N-terminal amino acids of native bovine rhodanese in combination with the chaperone DnaJ specifically inhibit s release factor- and stop codon-dependent hydrolysis of N-formylmethi onine from N(formyl)-methionyl-tRNA bound with AUG to salt-washed ribo somes. Neither the peptide nor DnaJ by itself causes this inhibition. The N-terminal peptide and DnaJ both singularly and combined do not af fect the peptidyltransferase reaction per se. The total amount of rhod anese synthesized in the cell-free coupled transcription-translation s ystem is reduced by the peptide, with concomitant accumulation of full -length enzymatically inactive rhodanese polypeptides on ribosomes. In combination with DnaJ, the N-terminal polypeptide inhibits the termin ation and release of full-length rhodanese peptides that have accumula ted on Escherichia coli ribosomes during the course of uninhibited cou pled transcription-translation in the cell-free system. This inhibitio n appears to involve release factor 2-mediated termination at the UGA termination codon in the coding sequence for rhodanese. It is suggeste d that the N-terminal peptide inhibits the binding of the release fact or to ribosomes. These data appear to provide the first report of diff erential inhibition of the termination reaction on ribosomes without i nhibition of the peptidyltransferase reaction and peptide elongation.